KR100778648B1 - A stack of polymeric membrane fuel cells - Google Patents

Abstract

The present invention relates to a stack of polymer membrane fuel cells, wherein in the stack of polymer membrane fuel cells of the present invention, the removal of heat generated by the generation of electrical energy and the humidification of ion exchange membranes used as an electrolyte are introduced from a single hydraulic circuit. Obtained by direct injection of water. Thus, the stack is made smaller, cheaper and easier to operate.

Fuel Cell, Cooling, Direct Injection, Water, Reticulated Members

Description

Stack of Polymeric Membrane Fuel Cells

TECHNICAL FIELD The present invention relates to a fuel cell, and more particularly, to a fuel cell using a polymer membrane as an electrolyte.

Fuel cells are electrochemical generators of electrical energy in the form of direct current, while they are fuels (eg light alcohols such as methanol or ethanol or gaseous mixtures containing hydrogen) and oxidants (eg , Free energy in the reaction of air or oxygen), without its complete deterioration, and thus not bound to the limitations of the Carnot cycle. In order to achieve a good conversion of chemical energy into electrical energy, the fuel is oxidized at the anode of the cell simultaneously with the release of electrons and H ⁺ ions, and the oxidant is reduced at the cathode, where H ⁺ Ions are absorbed The two poles of the generator must be sequestered by a suitable electrolyte, which allows the continuous flow of H ⁺ ions from the anode to the cathode, while at the same time hindering the transfer of electrons from the one pole to the rest of the electrodes. Maximize the potential difference between This potential difference actually represents the driving force of the process itself. The fuel cells are regarded as a good alternative to conventional power generation systems, especially in terms of their extremely desirable environmental effects (forming water as only by-products without pollution emissions and noise), which are fixed in various sizes. It is used both in the field of power generators (power stations, backup power generators, etc.) and in mobile applications (electric vehicle applications, automotive energy generation or auxiliary energy in space, submarines and navy).

Its rapid start-up and the speed of achieving optimum operating conditions, high power density and harsh thermal cycles (in fact, of all conventional fuel cells, polymer electrolyte fuel cells have the lowest operating temperatures (typically 70-100 ° C.) And the inherent reliability associated with both the absence of corrosion and the small number of moving parts, the polymer membrane fuel cells offer additional advantages over other fuel cells.

The polymer electrolyte used for this purpose is partly composed of ion exchange membranes, more specifically cation exchange membranes, ie groups which cause acid-base hydrolysis resulting in separation of electrical charges. Functionalized chemically inert polymers, wherein hydrolysis more clearly involves the release of cations (cations) and the formation of fixed negative charges on the polymers that make up the membrane. Porous electrodes are applied on the surface of the membrane, which causes the reactants to flow through it until it reaches the membrane interface. A catalyst is applied on the electrode and / or membrane side, for example, as platinum black, which is good for the corresponding half reaction of fuel oxidation or oxidant reduction. This arrangement also provides for a continuous flow of cations when a potential gradient is formed between the two surfaces of the membrane and the external electrical circuit is closed at the same time, in which case the transfer, as described above, The cation being H ⁺ ions is the potential difference that occurs when the anode feeds a splice with a lower electrochemical potential and the cathode feeds a splice with a higher electrochemical potential, the external circuit as soon as the external circuit is closed. Induces protonic conduction across the electron flow (i.e. current) across it.

Quantum conduction is an essential condition for the operation of a fuel cell and is one of the crucial parameters for evaluating its efficiency. Once the electrical circuit is closed with an external resistive load using the generated electrical output, insufficient quantum conduction causes a significant drop in the potential difference (voltage drop in the cell) of the electrodes of the cell. This in turn leads to an increase in reaction energy deterioration with respect to thermal energy and a continuous decrease in fuel conversion efficiency.

, 미국, 고어(Gore)사의 상표 Gore Select

, 일본, 아사히 체미컬스(Asahi Chemicals)사의 상표 Aciplex

로 상품화된 공업 연료 전지들에 널리 사용된다. 이와 같은 모든 막들은 양자 전도를 가능하게 하는 전하의 분리가 가수분해 메카니즘(hydrolysis mechanism)에 의해 설립된다는 동작 메카니즘과 연계된 고유의 프로세스 한계에 의해 부정적인 영향을 받고 있으며, 이런 막들은 액상수가 존재할 때에만 그 전도성을 발생시킨다. 비록 연료 전지의 동작의 고유한 결과로서 물이 형성되지만, 그 범위는 특히, 충분히 높은 전류 밀도에서 작동할 때, 막의 소요 수화 상태(hydration state)를 유지하기에는 거의 항상 불충분하게 된다. Some cation-exchange membranes that provide optimum quantum conduction properties are available in the art and are manufactured by industrial fuel cells, such as the trademark Nafion of Dupont de Nemours, USA.

Gore Select, US, Gore

Trademark Aciplex of Asahi Chemicals, Japan

It is widely used in commercial fuel cells commercialized with. All of these membranes are negatively affected by the inherent process limitations associated with the mechanism of action, in which the separation of charges that enable quantum conduction is established by a hydrolysis mechanism, which, in the presence of liquid water, Only its conductivity occurs. Although water is formed as a unique result of the operation of the fuel cell, the range is almost always insufficient to maintain the required hydration state of the membrane, especially when operating at sufficiently high current densities.

In fact, operation at high current densities entails a reduction in investment costs for a given power output, but reduces the generation of higher amounts of heat and energy efficiency. In addition to limited thermal stability of ion exchange membranes, which are generally unsuitable for operations above 100 ° C., the removal of by-product water and consequent removal by release of inerts and unconverted reactants from the cell should be limited as much as possible. In light of this, large amounts of heat generated in fuel cells operating at actual current densities (eg, between 150 and 1500 mA / cm 2) must be efficiently removed to allow thermal control of the system. In addition, since the voltage at the poles of a single fuel cell is too small for practical use, as disclosed in US Pat. No. 3,012,086, the cells are typically electrically connected in series by bipolar junctions. It is assembled in a filter-press arrangement that supplies the reactants in parallel. In such fuel cell arrangements, commonly referred to as " stacks, " the problem of heat removal is increased compared to the case of a single cell, and compared to the case of a single cell capable of taking advantage of heat dissipation through the outer walls. The problem of heat removal is increased.

For this reason, all designs of conventional fuel cells provide circulating fluids to hydraulic circuits suitable for heat removal by thermal exchange. Such fluids may be provided with serpentines, such as snakes, formed in appropriate portions or bipolar plates inserted between single cells electrically connected therewith, both of which are The composition of the stacks is further complicated and the weight and volumes are increased to reduce power density, which is a highly demanded factor, especially when applied to a vehicle.

An easier solution in this respect is described in PCT patent WO 98/28809, in which a cooling fluid circulates at the periphery of the bipolar plate adjacent to the active surface of the cell. In this way, however, a transverse temperature profile is formed in the membrane central region that operates at temperatures higher than the temperature of its surrounding regions, creating a potentially very dangerous thermal gradient for the integrity of the membrane itself.

Finally, even if the heat removal range required to set the system temperature below 100 ° C is achievable, concurrent water drain from the fuel cell stacks ensures that the resulting solution maintains sufficient valence levels of the membranes. Remains too high to do; Therefore, conventional stack designs further introduce a second auxiliary system to the cooling system which provides for injecting the additional amount of water required into the generator. Such a circuit typically pre-reacts the reactants at the inlet of the anodical and the cathodic compartments of the fuel cells, for example by diffusion of water vapor through the appropriate membranes in the auxiliary cells or by bubbles of liquid water. Is provided to singer in. This second circuit also entails an apparent increase in weight, volumes, and investment costs, and also the extreme consequence that excess liquid in the battery compartments blocks access of gaseous reactants to the surface of the electrode. The amount of water to be provided to the system for this electrode must be strictly controlled. Although indirect, the only way to regulate the water supplied by the system is to control the temperature of the water itself, and thus control its vapor pressure. This, in turn, requires temperature control of the hydrolysis system of the fuel cell stacks and further complicates the structural design.

A better solution for ensuring adequate water supply to the reactant stream is disclosed in EP 316 626, which discloses, for example, water atomized therein by an ultrasonic aerosol generator. Humidification of the reactant stream is carried out by spraying. This solution partly eliminated the need to cool the stack by the burdensome auxiliary heat exchange circuit, because part of the water supplied thereto evaporated inside the cell, thereby removing a significant amount of heat. However, this system is expensive and has the negative effect of the underlying defects exhibited by the structural complexity associated with the aerosol generator, which consumes a certain portion of the electrical output generated by the fuel cell.

Additionally, especially in the case of stacks with high current densities and a large number of cells, the time the water is present in the cell is too short to ensure simultaneous cooling of the stack and wetting of the membrane without the use of auxiliary circuits.

In addition, when adding atomized water or wetting the reactants prior to sending the reactants to the inlet manifold, condensation or water droplets of some water may be formed therein, and some cells of the stack This results in supplying an excessive amount of water to the fields (generally closer to the reactant inlet) and insufficient water to some other cells (generally those farther from the reactant inlet).

The present invention relates to a fuel cell stack comprising a reticulated electrically thermally conductive material sandwiched between an electrode face and a bipolar plate as disclosed, for example, in US Pat. No. 5,482,792, wherein the wetting of the reactants Superthermal control is achieved by a single circuit direct injection of the appropriate flow of water, which partially evaporates inside the mesh material to utilize the large surface and its thermal conductivity to effectively extract heat from the electrodes.

In one embodiment of the invention, the injection point of water in the gaseous flow is located downstream of the reactant inlet manifold.

In another embodiment, the spray point is located in a counterpart of the outer periphery of the mesh material in a region physically separated from those to which reactants are fed.

In another embodiment, water is sprayed corresponding to the recesses formed inside of the mesh material.

In another embodiment, the water is sprayed corresponding to serpentine-shaped serpentines, such as a snake provided inside the mesh material, and flows along its entire surface.

In another embodiment, the water is sprayed corresponding to offset double comb-shaped recesses provided inside the mesh material.

1 shows an overview of a membrane fuel cell stack according to the invention, assembled in a filter-press arrangement.

2A shows an overview of a membrane fuel cell stack of the prior art, assembled in a filter-press arrangement.

2b shows a bipolar plate of the prior art;

3, 4, 5, and 6 illustrate various forms of gaskets for fuel cells.

7, 8, 9 and 10 illustrate various forms of mesh elements for connection between electrodes and the bipolar plates and the distribution of fluids inside the fuel cell stacks.

With reference to the accompanying drawings will be described in detail the present invention.

Referring to FIG. 1, each of the unit cells 1 representing a repetitive unit of the module assembly in the filter-press arrangement proceeds from the inside to the outside, with an ion exchange membrane 2 and a pair of porous electrodes. , A pair of catalyst layers 4 formed at the interface between the membrane 2 and the electrodes 3, a pair of electrically conductive mesh elements 5, and a pair of peripheral seals Gaskets 6 and a pair of bipolar plates 7 defining the boundaries of the unit cell 1. The mesh element 5 has a minimum porosity of 50%, serves to electrically connect the bipolar plates 7 to the electrodes 3, and to form a gaseous reactant and humidification water. water, and the humidifying water is subdivided finely through the entire thickness of the mesh element, thus providing good evaporation inside the entire volume of the chamber defined by the bipolar plate 7 and the electrode 3. do. Appropriate apertures on the outer circumferential region of the bipolar plates 7 and the outer circumferential region of the gasket 6 are, in the juxtaposition of the above-described components, only two upper manifolds, shown in the figure. 8), wherein the two upper manifolds can be used to supply reactants, and also form two lower manifolds 9, only one is shown in the figure, and the lower manifolds create Water and unconverted portions of the gaseous water activators and reactants. Optionally, the lower manifold 9 can be used as a supply duct and the upper manifold 8 can be used as an outlet duct. In addition, one of the two reactants is fed through one of the upper manifolds 8, the corresponding lower manifold is used as the outlet, the remaining reactants are fed through the remaining lower manifold 9, and the corresponding It is also possible to use the upper manifold 8 as an outlet.

Outside the unit cell 1 assembly in the filter-press arrangement, there are two end plates 10, one of which is a fitting for hydraulic connection to the manifolds 8, 9, not shown in the figure. They have fittings, both of which have suitable holes for tie-rods used to clamp the complete stack, not shown in the figure.

2A and 2B, each unit cell 1 'constituting the repeating unit of the module assembly of the filter-press arrangement proceeds from the inside to the outside, with an ion exchange membrane 2' and a pair of porous electrodes. (3 '), a pair of catalyst layers (4') formed at the interface between the membrane (2 ') and each of the electrodes (3'), a pair of planar gaskets (6 ') for hydraulic sealing, It includes a pair of bipolar plates 7 'defining a boundary of the unit cell 1'. The bipolar plates 7 'have a ribbed profile 11, the protrusion of which ensures electrical continuity through the stack, and the recess allows the circulation of gases and water. Appropriate openings in the outer circumferential region of the bipolar plates 7 'form two upper manifolds 8', in which only one is shown in the figure, in the juxtaposition of the components described above, the two upper manifolds. Can be used to supply the reactants, and also forms two lower manifolds 9 ', in which only one is shown in the figure, the lower manifolds producing water, gaseous inerts and reactants Can be used to release unconverted portions of the two. Even in this case, it is possible to reverse the functions of the upper and lower manifolds.

Outside the unit cell 1 'assembly in the filter-press arrangement, there are two end plates 10', one of which is hydraulic for the manifolds 8 ', 9', not shown in the figure. There are fittings for the connection, both with suitable holes for tie-rods used to clamp the complete stack, not shown in the figure.

Referring to Figures 3, 4, 5, and 6, some embodiments of the gasket 6 are shown, the gasket having an upper hole 12 that forms the upper manifold 8 by juxtaposition in the filter-press arrangement. ), A lower hole 13 that forms the lower manifold 9 by juxtaposition in the filter-press arrangement, a housing for the mesh element 5, and optionally one or more for spraying water 15. It includes a channel.

Referring to FIG. 7A, one embodiment of a mesh element 5 made of a flattened expansion sheet with a rhomboidal mesh is shown, and in FIG. 7B a planar fine net with a square mesh is shown. .

8, 9 and 10, several embodiments of meshed devices are shown, which are made of deformable metallic material, such as metal foam, and in the examples of FIGS. 9 and 10 suitable channels for water spraying. Concave portions 16, which serve as a film, are formed inside the metallic material, for example by cold-pressing.

First embodiment

Two stacks made of 15 single cells 1 and one of 30 single cells 1 are manufactured according to the concept of FIG. 1, and install the following components.

115인 이온 교환막(2)-Nafion for sale by Dupont de Nemores

115 phosphor ion exchange membrane (2)

라는 상표명으로 이-테크 인코포레이티드(E-TAK Inc.)에 의해 판매되는 전극(3)ELAT, activated by a catalyst layer 4 made of platinum particles supported on activated carbon, with an active surface of 200 cm ²

Electrode (3) sold by E-TAK Inc. under the trade name

Mesh element 5 made of nickel foam as shown in FIG. 8 with pores comprised between 1 and 3 mm

A gasket 6 according to the concept of FIG. 3.

-Bipolar plate (7) made of stainless steel sheet of 2mm thickness

An aluminum end plate 10 electrically connected to a bipolar plate 7 of external cells, with current collecting sockets connected to a variable resistance load.

The stacks are connected to gaseous reactant sources and external circuits through appropriate fittings mounted on one of the end plates 10, wherein the external circuits are demineralized water thermally set to a predetermined temperature by a heat exchanger. Is circulating. Through these connections, the stacks are connected to the positive electrode (anode) by means of an upper manifold 8 obtained by juxtaposition of the filter-press structure of the upper holes 12 and the openings in the corresponding bipolar plates 7. ) Receives a mixture containing 70% of hydrogen and air at the cathode (cathode). The same manifold 8 receives a stream of demineralized water from the corresponding circuit, the flow rate of which is regulated according to the dynamic response of the system, if necessary. The stacks do not have auxiliary cooling in addition to being supplied to the manifold 8 by evaporation of the injected water.

The stacks are operated for 12 hours at a current density of 300 mA / cm ² , regulating the temperature of the cells to 70 ° C. and monitoring the voltage of a single cell. The amount of water flow is manually regulated to maximize the voltage of the single cell. At the end of this manual regulation, a voltage comprised between 715 and 745 mV is detected on each cell of both stacks. In a 30 cell stack, the cells with the lowest voltage values are statistically distributed farther from the water inlet (tail cell) and end plates connected to the reactants, and after an hour of operation, the voltage of the single cell Is generally constant.

The resistive load applied to the end plates 10 is then changed to draw a current density of 600 mA / cm ² from the two stacks. At this time, 15 cell stacks maintain stable operating conditions, single cell voltage is between 600 and 670 mV, the lowest values are statistically distributed among the tail cells, and most preferably, 30 cell stacks are local. Shut-down after about an hour, because the voltages exhibited by the end cells as a result of overheating continue to decrease.

Prior to spraying the same water into the upper manifold 8, the same test was repeated by spraying water with the ultrasonic aerosol generator. In all cases, there was no change in performance.

First Comparative Example

According to the concept of FIG. 2, fifteen fuel cell stacks are manufactured according to the prior art.

The stack has the following components.

115 이온 교환막(2')-Nafion for sale by Dupont de Nemores

115 ion exchange membrane (2 ')

전극(3')ELAT sold by E-Tech Incorporated, activated by catalyst layer 4 made of platinum particles supported on activated carbon with an active surface of 200 cm ²

Electrode 3 '

A planar sealing gasket 6 'having the same thickness as the electrode 3'

Bipolar plate (7 ') made from ribbed graphite sheet (5' thick)

A copper end plate 10 'electrically connected to a bipolar plate 7' of external cells, with current collecting sockets connected to a variable resistance load.

Similar to the embodiment described above, the stacks are connected to the supply circuit and the external circuit of the gaseous reactant through suitable fittings mounted on one of the end plates 10 ', which are connected by a heat exchanger. Demineralized water thermally set to a predetermined temperature is circulated. Through these connections, the stacks are supplied by the upper manifold 8 'to a mixture containing 70% of hydrogen at the anode (anode) and to the air at the cathode (cathode) and to the flow of demineralized water. Is supplied from the corresponding circuit to the same manifold 8 '. The stacks do not have auxiliary cooling in addition to that provided by the evaporation of water injected into the manifold 8 '. Despite all attempts to regulate the amount of water flow in the same manner as described in the above embodiment, a current of 300 mA / cm ² is due to the tendency of the voltages of some cells to be randomly distributed and exhibit a decrease with time due to overheating. It was impossible to reach the density. By reducing the current density, it was possible to obtain a stable operation of 70 mA / cm ² , at which value the voltages of each single cell were distributed in the range contained between 800 and 550 mV, and with the ultrasonic aerosol generator of the above-described embodiment When spraying, it was possible to increase the current density to 100 mA / cm ² , but it was impossible to further improve the current output. The results of these tests show poor uniformity of water injection among the multiple cells in the stack, and the irregular distribution of water inside the ribbed structure inside each cell, and spraying water upstream somewhat alleviates this problem. In other words, it does not have the same efficiency as the fine fragmentation over the entire volume of the battery generated by the mesh device of the above-described embodiment.

Second embodiment

The two stacks of the first embodiment receive water and gaseous reactants through the lower manifold 9 and use the upper manifold 8 for discharge. Under these conditions, it is possible to operate 30 cell stacks at 600 mA / cm ² , although five tail cells remain at a voltage of 600 mV or less. At the same current density, the voltages of the 15 cell stacks are distributed in a range comprised between 650 and 670 mV, although the maximum value is close to that of the previous experiment where injection is performed through the upper manifold, The distribution resulted in a more homogeneous. The above description shows that when a plurality of cells are fed in parallel through a manifold located at a higher level, a portion of the water may be collected at the bottom of the manifold itself, and subsequently the inlet of the group of cells proximate to the water jetting point. It is due to the fact that it can fall off. In the case of injection from the bottom, water does not fall into the cells, but instead is sucked by the inlet gas to provide a more uniform flow inside each single cell.

Third embodiment

The tests of the first and second embodiments were repeated by supplying pure hydrogen as fuel, closing the outlet manifold on the anode side, and spraying water only on the air inlet manifold. In both cases, the performance of the stack was observed to be substantially the same as the previous case, and it was found that the cell voltages rose slightly due to the increase in the molar fraction of the fuel. In addition, in the case of total consumption of pure fuel at the anode (dead-end operation), it was sufficient to humidify only the oxidant flow.

In this case, atomizing water upstream with the ultrasonic aerosol generator did not produce any positive effect.

Fourth embodiment

The thirty cell stacks of the previous embodiment were rotated 35 ° about their major axis, so that for each air-fed gasket 6, the lower hole 13 was placed at a lower level relative to its initial position, resulting in As a result, the entire lower manifold 9 on the air side is at a lower height relative to its initial level. The stack is then supplied with air from the corresponding lower manifold 9, to which water is sprayed as in the previous embodiment. Pure hydrogen is supplied from the corresponding lower manifold 9 so that it is consumed entirely without any humidification, and closes the associated upper manifold 8 in accordance with dead end mode operation.

Fifth Embodiment

According to the concept of FIG. 1, 45 cell stacks are manufactured according to the prior art, and have the following components.

라는 상표명으로 판매되는 이온 교환막(2)Gore Select by Gore, USA

Ion exchange membranes sold under the trade name (2)

라는 상표명으로 판매되는 전극(3)ELAT by US E-Tech Incorporated, which has an active surface of 900 cm ^{2 and} is activated with a catalyst layer 4 made of platinum particles supported on activated carbon.

Electrodes sold under the trade name (3)

For a bipolar plate 7 with a planar fine net for the electrode 3 as shown in FIG. 7b with a square mesh with a side length of 1 mm, and a romboidal mesh with a side length of 3 mm. Mesh element 5 fabricated by superimposing a flat expansion seek as shown in FIG. 7A, both the inflatable sheet and the planar mesh are made of stainless steel AISI 316L

A gasket 6 according to the concept shown in FIG. 4.

-Bipolar plate (7) made of stainless steel sheet of 2mm thickness

An end plate 10 made of aluminum which is electrically connected to the bipolar plate 7 at each end of the stack, with current collector sockets connected to a variable resistance load.

The stack is connected to the supply and external circuits of the gaseous reactants via suitable fittings mounted on one of the end plates 10, where the demineralized water is thermally set to a predetermined temperature by a heat exchanger. It is becoming. Through these connections, the stacks are at the anode (anode) by means of a lower manifold 9 obtained by juxtaposing the corresponding holes of the bipolar plate 7 of the filter-press structure with the lower holes 13. Pure hydrogen and air are supplied from the cathode (cathode). The flow of demineralized water, whose flow rate is regulated as necessary according to the dynamic response of the system, is fed from the relevant circuit to the injection channel 15. The stacks do not have an auxiliary cooling additional to that provided by the evaporation of the water supplied to the injection channel 15.

The stack is operated for 12 hours at a current density of 700 mA / cm ² , regulating the temperature of the cells to 75 ° C. and monitoring the voltage of a single cell. The amount of water flow is manually regulated to maximize the voltage of the single cell. At the end of this passive regulation, all cells in the stack exhibit a voltage comprised between 680 and 700 mV, which becomes stable over time. This test is shown in FIG. 4 where mixing of two fluids occurs in a smaller duct downstream of the inlet manifold, compared to the type of gasket used in the previous embodiments to determine the mixing of water and gas in the inlet manifold. It allows us to verify that it is better to use a full gasket.

Also in this case, it was verified that atomization of the water sprayed into the air stream supplied to the channel 15 did not provide any good effect.

Sixth embodiment

Forty-five fuel cell stacks were assembled identically to one of the previous embodiments, and gaskets corresponding to those shown in FIG. 5 were used. This design form provides independent supply of gas and water streams in parallel directions to each other, which ensures a more even distribution of water inside a single cell after being introduced into the mesh element 5. Under the same operating conditions as the fifth embodiment, after operating at 700 mA / cm ² , the stack exhibits cell voltage values comprised between 700 and 715 mV.

Seventh embodiment

The 45 fuel cell stacks are assembled identically to one of the previous embodiments, except that the gasket corresponding to that of FIG. 6 and the mesh element 5 made of the same nickel foam as that of the first embodiment are used. The stack is connected to feed reactants from the upper manifold 8 and to drain the same from the lower manifold 9. In this gasket form, the injected gas and the water stream are separated until after they are inserted into the mesh element 5 and are mixed in directions perpendicular to each other. In this case, in order to ensure sufficient humidification of the upper region of the mesh element, the water flow is largely introduced into the channel, and only a small amount is divided so as to be introduced into the upper manifold 8 used to feed the battery. The portion of water sprayed into the channel 15 is set to about 90% of the total, and in no case less than 80%. Operated at 700 mA / cm ² under the same operating conditions as the fifth and sixth embodiments, the stack exhibits a battery voltage value comprised between 710 and 730 mV.

Eighth embodiment

The 45 fuel cell stacks are assembled in the same manner as the sixth embodiment, except that the mesh element 5 made of nickel foam as shown in FIG. 9 is used. In this case, the deformability of the metal foam is utilized to form two small channels or recesses 16 for good distribution of water in a direction substantially parallel to the gas flow, which channels the entire surface of the foam. It has a serpentine form, like a snake across it. In order to form the recesses 16, it is sufficient to cold roll a metal wire having a predetermined thickness into a metal foam. In this case, a sinuous shape, such as a snake of 3 mm width, was obtained by cold rolling a steel wire having the same thickness. It is obviously possible to form a serpentine shape, such as a single snake or two or more serpentine shapes, to be fed from a single channel 15. Under the same operating conditions as the fifth, sixth and seventh embodiments, this stack operated at 700 mA / cm ² exhibits battery voltage values comprised between 715 and 730 mV.

9th embodiment

The 45 fuel cell stacks are assembled in the same way as in the seventh embodiment, except that only the gasket 6 corresponding to that of FIG. 6 and the mesh element 5 made of the nickel foam illustrated in FIG. 10 are used. Even in this case, the permanent deformation of the metal foam is utilized to form two small channels for good distribution of water, but in this case, however, a series of supplying water in a direction substantially perpendicular to the direction of the gas flow. The offset double comb shaped shape is selected to form parallel ducts. This improves the overall pressure drop inside the mesh, causes gaseous reactants to follow more twisted paths, distributes gaseous reactants along the entire active surface of the cell, and avoids stagnation or depletion areas. Let's do it. Under the same operating conditions as the fifth, sixth and seventh embodiments, this stack operated at 700 mA / cm ² exhibits cell voltage values comprised between 730 and 740 mV.

Although the present invention has been described with reference to specific embodiments, the above embodiments are not intended to limit the invention and the scope of the invention is defined in the appended claims.

Claims (21)

A stack of polymer membrane fuel cells supplied with a gaseous reactant, The membrane separates the annodic compartment from the cathodic compartment, Bipolar plates, gaskets optionally provided with channels for supplying and discharging fluids, porous electrodes, catalyst layers interposed between the membranes and the electrodes, and for supplying the flow of reactants Manifolds, unreacted portions of the reactants and inerts and manifolds for releasing the generated water and hydraulic circuits for injecting water flow inside one or more compartments of the cells One or more injection points, The water flow simultaneously provides humidification of the membranes and removal of generated heat, At least one compartment of the cells supplied with water and reactants introduced from the injection point comprises an electrically and thermally conductive mesh element interposed between the electrodes and the bipolar plates, the mesh element being the gas A stack of polymer membrane fuel cells, characterized in that the water flow is distributed through the entire volume occupied by the soluble reactant. The stack of polymer membrane fuel cells of claim 1, wherein the water injection point is located outside the one or more compartments. The stack of polymer membrane fuel cells of claim 2, wherein the water injection point is located at the inlet of the manifold for supplying the flow of reactants. 4. The stack of polymer membrane fuel cells as recited in claim 3, wherein said manifold for supplying a flow of reactant is a lower manifold. 5. The stack of polymer membrane fuel cells in accordance with claim 4, wherein said stack rotates about its major axis and said manifold is located at its lowest position. The stack of polymer membrane fuel cells according to any one of claims 1 to 5, wherein only one of the compartments of the cell is supplied with water. 7. The stack of polymer membrane fuel cells as recited in claim 6, wherein the only one compartment supplied with water is a cathodic compartment. 3. The stack of polymer membrane fuel cells according to claim 2, wherein the water injection point is located in a channel formed in the gasket, downstream of the manifold for supplying the flow of reactants. The stack of polymer membrane fuel cells as recited in claim 1, wherein the water injection point is located inside the cells. The stack of polymer membrane fuel cells according to claim 8, wherein the water injection direction is parallel to the direction of flow of the reactants. The stack of polymer membrane fuel cells of claim 8, wherein the water injection direction is orthogonal to the flow direction of the reactants. The stack of polymer membrane fuel cells according to claim 1, wherein the mesh element can be deformed by cold rolling. The stack of polymer membrane fuel cells according to claim 12, wherein the mesh element that can be deformed by cold rolling is a metal foam. The stack of polymer membrane fuel cells according to claim 13, wherein the metal foam comprises nickel. 13. The stack of polymer membrane fuel cells in accordance with claim 12, wherein said mesh element comprises at least one recess for water distribution. 16. The stack of polymer membrane fuel cells in accordance with claim 15, wherein said at least one recess is obtained by cold rolling. The stack of polymer membrane fuel cells of claim 15, wherein the direction of the at least one recess is parallel to the reactant flow direction. 18. The stack of polymer membrane fuel cells according to claim 17, wherein the recesses have a serpentine shape. The stack of polymer membrane fuel cells of claim 15, wherein a direction of the one or more recesses is orthogonal to the reactant flow direction. 20. The stack of polymer membrane fuel cells in accordance with claim 19, wherein said recess is disposed according to an offset double comb-shaped geometry. delete

Images